The present application relates to the art of gas separation. It finds particular application in conjunction with pressure swing adsorption oxygen concentrators for separating oxygen from atmospheric air and will be described with particular reference thereto. However, it is to be appreciated that the present invention is applicable to the purification and separation of other gases.
Heretofore, oxygen has been separated from atmospheric air by selective adsorption. Atmospheric air was cyclically pumped into one of a pair of beds filled with a physical separation material. The physical separation material permitted the less strongly adsorbed molecules to pass therethrough while trapping or retaining the more strongly adsorbed molecules. A 5A zeolite material passes oxygen and argon but adsorbs nitrogen, carbon dioxide, and water vapor. Other physical separation materials adsorb oxygen and pass nitrogen and argon, and other combinations of gases. When the trapping or adsorption capacity of the bed was substantially met, i.e. the bed was substantially saturated, the air was pumped to the second bed while the first bed was evacuated or cleansed of adsorbed molecules.
Commonly, gases were transferred between the beds. For example, a pressure equalization valve might be operated to equalize the pressure between the beds to conserve the energy in the compressed gases. Commonly, while the saturated bed is being evacuated of adsorbed material, a small amount of primary product gas, e.g. oxygen, from the other bed is fed back through check valves and restrictors.
The oxygen or other separated gas(es) were stored in a primary product gas reservoir. More specifically, a second compressor commonly increased the pressure of the primary product gas and stored it in the primary product gas reservoir. When the reservoir was filled to a preselected pressure, separation of oxygen or other primary product gas was stopped.
One of the problems with the prior art is that while the system was stopped, a small amount, of leakage inherent in most commonly available valves allowed the beds to come into pressure equilibrium. The pressure equilibrium was usually at least in part attributable to air and adsorbed secondary product gases equalizing themselves in the two beds. When the primary product reservoir became low and the separator was restarted, the air and secondary product gases from one of the beds would be supplied as primary product gas during the initial fractional cycle portion. In practice, the output primary product gas tended to be below optimum purity for the first full cycle or two. Yet, this less than optimally pure primary product gas was supplied to the primary product reservoir reducing the purity of the gas therein.
Another problem in the prior art resided in the second compressor for compressing the relative low pressure primary product gas from the molecular sieve beds to the high pressure of the primary product storage tank. In large volume or high pressure applications, the second compressor is normally a piston-type compressor or pump. Diaphragm compressors or pumps are normally only available for low volume and low pressure applications. In a piston-type compressor, the piston draws primary product gas in during the downstroke. The reduction in pressure caused by the downstroke also causes some leakage between the cylinder and the bore. More specifically, the negative pressure draws air from the crankcase of the second compressor around the piston and into the primary product gas. This compressor leakage again reduces the purity of the primary product gas.
The present invention contemplates a new and improved gas separation system and primary product gas delivery system which overcomes the above-referenced problems and others.